Process and apparatus for taking x-ray pictures of parts of the human body



Feb. 13, 1940. STRAUSS ET AL 2,190,389

PROCESS AND APPARATUS FOR TAKING X-RAY PICTURES OF PARTS OF THE HUMAN BODY Filed July 7, 1937 2 Sheets-Sheet 1 a O 6 I 9 a mmlnnmmlm IIIIIIII W.

'l/IIIIIIA Feb. 13, 1940. s, STRAUSS AL 2,190,389

PROCESS AND APPARATUS FOR TAKING X-RAY PICTURES OF PARTS OF THE HUMAN BODY Filed July 7, 1937 2 Shets-Sheet 2 Fig.2

F r W "A in l llllllllllllllllll Q i i 1 Patented Feb. 13, 1940 UNITED STATES PATENT OFFICE X-RAY PICTURES OF PARTS HUMAN BODY OF THE Siegmund Strauss and Louis Weisglass, Vienna, Austria Application July 7, 1937, Serial No. 152,410 In Austria July 8, 1936 20 Claims.

In taking photographic X-ray pictures of the human or animal body, especially of the heart or of the lungs, it is frequently observed that the picture shows indistinct outlines because of the heart beat movement, the time of exposure, say one half to one second in the case of usual X-ray machines of medium power, being relatively long in comparison to the heart movement. Even if very powerful tubes and machines are used, which allow the reduction of the exposure time to about of a second, distinct pictures are a matter of chance, if the X-ray machine is switched in by hand, the exact phase of movement of the heart, in which the exposure takes place being of great importance. During certain phases of its cyclic movement the heart and the adjacent body parts, such as the lungs, are moving with such high speed, that even the shortest exposure time, obtainable with the most powerful machines, would be too long to obtain clear and distinct pictures during this phase.

It is well known that the cyclic action of the heart comprises, in general, the following movements: Starting with its greatest dimension, the heart contracts itself first and compresses the blood during the systolic phase. This movement occurs with great rapidity during a very short period of time. Subsequently, the heart expands much more slowly to its greatest, diastolic position and remains in this state, termed the diastolic stop'or short diastole, during about 0.16 second in repose. This cycle is repeated periodically. The pulse beat is caused by a blood pressure surge immediately following the systole of the heart with a slight phase drift of about 0.1 second caused by the elastic properties of the conduit formed by the arteria. As a rule, the pulse beat occurs about at the end of the systolic movement of'the heart.

The invention aims to provide a method for taking X-ray pictures of the heart or of other moving parts of the human or animal body, which makes it possible to obtain, with X-ray machines of medium and even of small size, photographic pictures of the heart and the lungs etc, which are thoroughly unobjectionable, clear, distinct and well exposed For this purpose, according to the invention, the total BXDOSUIQ time required is divided into several short fractionary exposures, immediately following one after the other and efiected always in the same phase of the heart movement, for instance the diastolic stop, using automatic control of the ray-emission of the X-ray tube by the heart.

The invention further aims to provide a device for carrying out this process, which may also be used for taking single exposures in a certain phase of movement of the heart, this device making use of a novel time delay circuit for impulses making possible an automatic phase shifting and a very exact adjustment of the moment and the duration of the exposure. In the device according to the invention, only standard parts normally used in the electronic and telephone art are employed, this device being therefore inexpensive in manufacture and thoroughly reliable in operation.

In a special embodiment of the invention, novel means are provided, which ensure the correct operation of the device not only if used with persons having a fairly normal heart action, but also in the case of certain abnormal actions of the heart and the pulse, for example the socalled extra-systoles. If the person to be examined has a heart disease causing extra systoles, that is to say erratic double heart beats consisting of two beats occurring in succession and separated by a very short interval of time, the automatic phase shifter would effect the exposure following the extra systole in a wrong phase of the heart position, causing an indistinct picture. According to the invention, this drawback is overcome by intercepting the exposure following the extra systole by means of a special device, termed extra-systole trap.

Further objects of the invention are the provision of releasing devices for the exposure and if desired also for the movement of a secondary ray diaphragm (Bucky-diaphragm) with the object of automatically starting these movements always at the correct instant, independently of the skill of the operator.

A further object of the invention is to provide an integrating time measuring device termed exposure meter which records independently of the time and duration of the individual periods of exposure the total time of the exposures. This device may also be used to give a signal or to turn off the X-ray machine, when a predetermined number of periods of exposure or total duration of exposures has occurred.

The apparatus comprises primarily the following four parts represented schematically in the accompanying drawings:

I. A device for transforming the heart movements or pulse beats into electrical impulses.

II. An amplifier for amplifying said impulses and transforming the same into relay movements.

III. A device, hereinafter termed phase shifter,

, vising device.

for translating these relay movements with a desired and exactly adjustable time delay for alteration of the phase condition to a time switch for the X-ray machine, and

IV. A device for recording and measuring the exposure time and for switching off the X-ray machine herein called an exposure meter.

Moreover, the hereinbefore mentioned extrasystole trap, a releasing device with the exposure key and a starting for the Bucky-diaphragm may be provided.

In the accompanying drawings, Fig- 1 shows a circuit diagram of the parts IIV, Fig. 2 a diagram of the extra-systole trap with the key, the phase shifter (III) being represented similarly as in Fig. 1.

In the embodiment represented in the drawings, the parts I and II correspond to similar devices described in our copending application Ser. No. 136,468, filed April 4, 1937 for a blood pressure and pulse frequency measuring and super- In the present case, the relay in the output circuit of the amplifier II does not or does not only control the direct reading frequency meter, according to our Patent No. 2,114,578, granted April 19, 1938, but the novel phase shifter and'further the X-ray machine,

the exposure meter IV and other devices.

" anode bend rectifier-amplifier.

If it is desired to indicate simultaneously the number of pulse beats per time unit by direct pointer deflection, the pulse frequency meter may be actuated together with the phase shifter. Theparts I and II, however, may be substituted by other arrangements adapted to actuate a relay in synchronism with the action of the heart, for instance by the well known arrangement of the electrocardiograph. In this case it is however necessary to use extensive shielding. :In the embodiment shown by way of example in Fig. 1, the pulse pick-up is effected by means of a compression cuff'or bag I applied to the pulse arteria on the wrist and inflated by means of the manometer M. This pressure and all the variations of the pressure are transmitted by means, of rubber hose and conduits to the diaphragm 2, directly acting upon a piezo-electric crystal 3. The crystal holder is pivotally mount ed and adjustable with considerable friction in a support L. The tension spring F tends to rock the crystal holder in a counter-clockwise direction, so that the crystal 3 always bears upon a pin S'attached on the diaphragm 2. Slow pressure variations, that is, zero point shiftings, merely cause an angular displacement of the crystal holder, as the friction of. the bearing will be over* come in this case, without altering the fiexion of the crystal. The crystalholder cannot, however, follow the blood pressure pulsations, because of the friction of the bearings and said variations generate electrical tensions acting upon the grid of the tube 4. The screw T allows the crystal to be lifted from the pin S, in order to avoid damage during transportation. i

The voltage surges generated by the crystal at each pulse beat act directly upon the grid of an amplifying tube 4, which is preferably directly coupled to an output pentode tube 5. In the plate circuit of said pentode the pulse relay 5 is arranged. The output pentode 5 is used as an The necessary grid bias of thistube is adjusted simultaneously isupplied by a glow lamp-voltage divider 8, which is supplied with direct currentof the polarity shown for instance by means of a usual rectifier operating from alternating current mains. The output pentode 5 has a separate filament transformer coil and its cathode circuit comprises a damping resistance 9, which serves to regulate the amplification factor. The phase shifter III is connected to the pulse relay 6, the armature of which is attracted at each pulsation. The phase shifter comprises first of all the two relays H1 and II. If the pulse relay 6 makes contact, a condenser iZ, normally laying across a direct current potential, is discharged through the relay I0, so that the latter responds for a short period. By closing its contact a, relay l0 charges, as it is actuated for a short period of time, a condenser 13 up to a predetermined voltage. The operation, as hereinbefore described is effectedwithout appreciable phase shift.

The purpose of the relay I0 is as follows: Under certain circumstances, it would be sufficient to control the charging of thecharging condenser l3 by the pulse relay 6 itself. But the movement of said pulse relay 6 does not take place quickly. Under certain. circumstances it may take from 0.2 to 0.3 sec. In this case, the charging condenser l3 would be exposed to the full voltage and its discharge could only start when the relay 6 had been restored so that the time lag would start with the restoring of relay 6 and the beginning of the exposure would depend upon the closing time of relay 6. By interposing the relay iii, the condenser i3 is connected tothe direct current source of potential only for a very. short duration and always at the very instant in source of current. A part of its charge flows over the resistance 14 to. the condenser l5, and thevoltage on the terminals of said condenser raises until the glow-lamp Iii lights up and the amount of electricity corresponding to the charge flows ofi through the same and the resistance 11., The period of time from the response of the relay to the ignition of the glow-lamp is only given by the amount of the resistance M, the charging voltage, the ignition voltage and the capacities being constant; this time delay may he therefore easily adjusted within the desired limits.

The voltage surge caused by the lighting of the glow-lamp causes a voltage drop on the resistance H, which is transmitted to the grid of the tube l8. This grid is preferably blocked by a condenser and connected by means of a leak resistance to a point of negative bias with respect to the cathode, for example, to the heating coil. Therefore, the tube Ill becomes conductive at each movement of the relay H) for a very short period of time which occursat an adjustable interval later than the response of said relay i0 and therefore than the pulse beat.

In the plate circuit of the tube I8 is arranged the relay II for switching in the X-ray machine with itspair of contacts 1'. In order to adjust the period of duration of the exposure, this relay is shunted by the condenser 2 and the variable resistance 2I. The lower'this resistance 21 is adjusted, the larger its restoringtime lag caused by the condenser 22 will be and the longer the exposure time willbe.

The resistance Il may be also adjustable and mechanically coupled to the resistance H for joint operation, in order to enlarge the range of exposure time.

The set of contact springs of the relay II has two more pairs 71 and s of making. contacts. One of said pairs of contacts, for example, s, controls the exposure meter IV, to be described later, and the other pair of contacts it short circuits the condenser I3, over the resistance 20 and the condenser I9 to discharge the same at each attraction of the relay II, that is to say at each lighting of the glow-lamp I6. This is necessary for the following reason:

If the glow-lamp I6 lights, the charging condenser I3 is not yet discharged to such an amount that a second recharge of the condenser I5 and another lighting of the glow-lamp would be impossible. Under these circumstances, repeated lightings at increasing intervals would occur. To avoid this, it is necessary to bring the voltage of the charging condenser I 3 down to an amount well below the lighting voltage of the glow-lamp I6, after the occurrence of the first lighting. This is done by bridging the condenser I9 over the charging condenser I3 by means of making contact of relay II. A resistance 29 shunted to this condenser discharges the same in the period of rest. In this manner, not only the otherwise unavoidable repeated lighting is avoided, but at Y the same time a time compensation is obtained in the following manner: The arrangement, as hereinbefore described, allows to obtain a predetermined time delay. If the arrangement would operate in such a manner that this time delay would be fixed, that is to say always the same, without consideration of the operating frequency of the relay 6, a change of the pulse frequency during the exposure would result in difierent phase conditions, because the required .phase shift, for instance between the pulse beat and the diastole, cannot be measured in absolute time units, as seconds, but only as a percentage of the duration of a pulse stroke. The time delay, measured in seconds, should therefore be the smaller, the more rapid the individual pulse strokes follow each other, that is to say the higher the pulse frequency.

This result may be obtained, at least to a certain degree, by said parallel condenser I9. At the moment of the lighting the charging condenser I3 is partly discharged in the manner described. In the following rest period the condenser I5, now in parallel to the glo-wdamp, begins to discharge itself back over the resistance I4 and recharges the former discharging condenser I3. The starting potential of the glowlamp condenser I5 at the moment of the current impulse given by the pulse relay 6 is therefore dependent on the state of discharge, that is to ,say depends on the time available for the discharge or in other words on the pulse frequency. Therefore, an automatic correction of the time delay of the phase is obtained in the correct sense, the starting potential of the condenser I3 being the higher, the shorter the time available between the individual impulses.

The exposure-integrator or. exposure meter IV comprises a condenser 26, which at each. attraction of the relay II is connected during the exposure over the resistance 24 to a source of. di-

this potential being given (the charging. voltage" being constant) by the amount of the resistance 24 and moreover by the total duration of the exposure, the potential remaining the same on the condenser 26 during the intervals between the exposures. The glow-lamp 25 is arranged in parallel with the condenser 25 and in series with the relay 23. The operation of said relay causes the short circuiting of the condenser 26 and by means of the contacts on the leads A the actuation of an optical or acoustical signal or the'automatic disconnection of the X-ray machine. It may be seen, that the glow-lamp 25 will light and therefore the relay 23 respond only if the potential of the condenser 26 is equal to the ignition voltage. The number and duration of exposures required to reach this point is higher, the higher the resistance 24 has been adjusted.

The operation of the device is very easy:

The cuff'l being applied to the arm of the patient, B being connected to the on and A to the. off circuit of the X-ray machine switch, a number of individual instantaneous exposures are automatically made, at each pulse beat and always in exactly the same phase relation. If the number of exposures necessary to thoroughly expose the film are made, the X-ray machine is automatically turned off. It is only necessary to adjust the resistance 24 according to the desired opacity of the film-picture, the resistance 2| according to the duration of the individual exposures desired or permissible for distinct pictures, and to set resistance I4 for optimal phase relation. This phase relation is now maintained almost independent from the pulse frequency.

In the case of an occasional extra-systole, instead of the normal single heart beat two beats occur in. immediate succession and accordingly the relays Ii and Ill are moved twice. In order to avoid in this case the exposure in the incorrect moment which would result in moved or indistinct pictures, the extra-systole trap intercepts the exposure immediately following the double stroke.

As shown by Fig. 2 the set of contact springs of the relay II contains for this purpose four pairs h, i, s and r of contact-making springs. One of these contact pairs controls the exposure meter IV, the other contact pair h short circuits at each actuation of the relay II, that is to say each time as the glow-lamp I8 lights up, the condenser I3 over the resistance 20 and the condenser I9, in order to discharge the same.

The extra-systole trap properly comprises a tube V having a condenser c between its grid and cathode. Said condenser e is charged by a source of direct current over the additional contact I) of relay IE and over the resistance 0, so that the condenser plate near to the grid becomes negative. In the plate circuit of the tube V a relay 9' with two breaking contacts k and i is arranged, said contacts being parallel to the con tacts h and i of the relay II. Contacts i and 21 short circuit the'condenser e, if the relay 9 is not actuated. Since the relay III is actuated by the discharge of the condenser I2, and therefore has an exactly predetermined closing time, each impulse causes the potential of e to rise to a certain value on the exponential curve representing the charge of a condenser plotted against time. In other Words, a first impulse of relay I0 causes a certain voltage on the condenser e, a second impulse causes a higher voltage, which is also ex-- actly' determined. The tube normally carries plate current. Now the characteristic of the tube and if desired a pre-set grid biasing voltage are so chosen, that the negative charge resulting after one impulse cannot yet block the plate current. After two impulses, however, the grid voltage is high enough to block the plate current and the relay g is restored. If two impulses occur within one normal pulse beat, that is to say an extra-systole occurs, the plate current of tube V'is blocked and the relay is restored, closing the contacts h and 1 Closing the contact h though, causes the short-circuiting of the charged condenser I3, said condenser normally effecting the phase-shifting process, so that the glow-lamp I6 cannot light up and the exposure is intercepted. At the same time, condenser c is which said condenser e receives in the case of ordinary activity of the heart, without extrasystoles, is not suiTlcient to block the tube V and is periodically absorbed by the short circuit at each exposure. I

It may be seen that the extra-systole trap does not involve a considerable complication of the device and may be built up, like this device, from normal components of the low tension and amplifier art. In operation, no special adjustment is required, the surgeon may eirect the photography or screen examination without taking care of a possible heart disease of the patient causing extra-systoles. In each case a thoroughly still picture on the screen, that is, a picture that will not flicker if the screen remains luminous for some time after its exposure to X-rays, is obtained or a distinct photographic record. If

-. an extra-systole occurs, the immediately following exposure will be intercepted and any disturbance of the picture on the screen, or indistinct outlines on the X-ray photograph are avoided. As in this case the exposure meter will not receive an impulse, the pre-set exposure duration or number of periods of exposures is automatically prolonged accordingly. This is true for the exposure meter described with reference to Fig. 1, which integrates the total exposure duration, as well as for the simplified embodiment of the exposure meter, recording only the number of exposures by means of an electro-mechanical counter.

In the drawings, there is also shown a further development of the device according to the invention, which has the purpose of making the operation more easy, especially in the case of an abnormal rapidity of the sequence of pulse beats. In order to start the exposures, the exposure key X is provided. This key may be depressed at any desired moment, except the m0- ment at which the exposure relay ll responds, because in this case the duration of the first exposure would be shortened in an indefinite manner. If the surgeon has some skill, he will be able to avoid this moment in depressing the key, as long as the pulse frequency is normal. In the case of a very high pulse frequency of say 120-140 the impulses are following each other with such rapidity that the contact may be closedv by chance just in the moment of response of the exposure relay and the above mentioned drawback may occur, so that the first exposure may be shortened in an indefinite manner. The arrangement hereinafter to be described aims to avoid this starting of the exposures by depressing the exposure key just within the duration of the response of the exposure-relay. For this purpose, relay ID has one additional contact k. In the circuit of said contact, a re,- sistance Z, a source of direct current and a' relay m are arranged. Relay l0 shortly responds during the systole, and accordingly relay m also shortly responds. The contact n of relay m ,is arranged in series with contact q of the exposure key X and this series combination is arranged parallel to contact is. Contact 0 of this relay is in series with contact p of the exposure key and with the making contactr of the exposure relay. The exposure takes place in the following manner:

At each systole, relay ID and relay m quickly respond. As long as the key X is not depressed, relay m immediately falls back again. If, however, said key is depressed and thereby contact q is closed, the next systolic impulse causes the actuation of relay m, which holds itself by means of the contacts n, q and k. Contact 0 is closed in this way and the X-ray exposures are started always adjusted for a full exposure period, irrespective of the moment at which the key X is depressed. Ii said key is depressed by chance just during the actuation of the exposure relay H that is to say a short interval of time after the impulse, relay m is only actuated at the next following impulse and the open contact 0 avoids immediate switching on ofthe X-ray machine R. In this manner, a mistake is made impossible, the surgeon may diepress the key at any desired moment and needs not use any attention for this operation.

If photographs of the lungs are to be made, his sometimes advantageous to employ a secondary ray diaphragm. As is well known it is necessary to move such secondary ray diaphragms during the exposure, because otherwise the lead gridwork would appear on the picture. If such a secondary ray diaphragm is used together with the device according to the invention, the diaphragm should be set in motion at the right moment. According to a further development of the invention, this is done automatically by means of a separate contact 11' on the relay Ill, arranged in series with a further contact 2 of the exposure key X and effecting the release of the secondary ray diaphragm by electrical means B. If now the key X is depressed, one oi the two contacts of the releasing device, for example, a, is preparatorily closed. The diaphragm still remains in its home position, the X-ray tube is not yet turned on, the contact 0 being still open. If now the next systole causes the actuation of relay I0,'the con tact y is closed and the diaphragm is set in motion. A short time afterwards, according 'to the time delay adjusted by means of resistance M, the first exposure is made, the diaphragm being already in motion at this moment.

The extra-systole trap is advantageous, if the just described key releasing device or the automatic release of the Bucky-diaphragm is em-' ployed, because this trap intercepts the start of the exposures, if an extra-systole occurs. In this case relay H is not actuated, so that contact 7' remains open and the exposures will start sensitive to ing cryst' tive to X I'ays, comprising making plurality of exposures of short duration on single iilm immediate succession during corresponding phases of successive heart movements. the moment of the individual ex posures being controlled by the heart-action sell by detecting body impulses dependent on the heart action, converting said impulses into elec- .tric impulses, actuating the X-ray lllflli 'n in response to said electric impulses, and delaying .the actuation of the X-ray .machine after the occurrence oi. each of said elect c impulses until the desired. phase of the h :t l'llQVE'lllel'ltS 2. In apparatus for making X-ray pictures of parts of the human or animal body, a piezoelectric crystal, means for applying force to said 3. In apparatus for making. X-ray pictures of parts of the human or animal body, an 2-I-ray macl'llne having switching relay, a compression curl adapted to be applied to the body or the patient, a manometer chamber, a hose-conduit connecting said compression curl to said manometer chamber, said chamber having a diapl agm forming one wall thereof, a piezo-electrio crystal, adjustable friction means for holda spring pressing said crystal against said diaphragm, an amplifier having said crystal connected in its input circuit and a relay moving in synchronism with the heart-beats connected in its output circuit, and an adjustable time delay device between the said relay and the switching relay oi the X-ray machine.

4. In apparatus according to claim 2 an amplier with direct lnterstage coupling, the plate of the tube of the first stage being in direct metallic connection with the control-grid of the tube of the second stage.

in apparatus for transmitting successive impulses with adjustable time delay, a first condenser, means for connecting said first condenser, upon occurrence of each impulse, for a short period to source of electric potential, an adresistance, second condenser, means permane tly connecting said second condenser to said Ill-st condenser through said adjustable resistance, an indicating device, responding only at a predetermined minimum voltage, and means connecting saio. indicating device in parallel with said second condenser.

E. In apparatus lor transmitting successive impulses with adjustable time delay, a first condenser, means for connecting said first condenser, upon the occurrence of each impulse, for a short period to a source of electric potential, an adjustable resistance, a. second condenser, means permanently connecting to said second condenser first condenser over said adjustable resistance, a relay device responding only at a predetermined rninimum voltage, and means connesting said indicating device in parallel to said second condenser.

7. Apparatus acccording to claim 5, in which the device responding at a predetermined minimum voltage is a glow-lamp, a thyratron or like tube, having in its circuit an indicating instrument.

8. Apparatus according to claim 5, in which means provided for discharging the first condenser at the first response of the device arranged in parallel to the second condenser, in order to avoid mutiple response.

9. Apparatus accordin to claim 5, in which n ans are provided for discharging the first conthe first response of the device arranged parallel to the second condenser, in order to avoid multiple response, said means comprisresistance with a shunt condenser.

10. in apparatus for making X-ray pictures of or the human or animal body, means for producing electrical impulses upon application of pressure variations thereto, means for applyblood pressure variations of the pulse to said impulse producing means, an amplifier having of second relay irrespective of the speed of operation of the said first relay.

il. in apparatus for making X-ray pictures of parts of the human. 01' animal body, means for nducing electrical impulses upon application or pressure variations thereto, means for app-lying blood pressure variations of the pulse to said :inipul producing means, a vacuum tube connects to receive said impulses in its grid circuit and having an actuating relay for the Xray machine connected in its plate circuit, a condenser and a variable resistance connected in parallel to said relay, for adjusting the delay of the restoring movement of said relay and thereby the exposure time.

12. In apparatus for integrally measuring the sum of any desired number of small periods of time and for effecting an indication or actuation after a predetermined adjustable total amount of time has been reached, especially for supervising the total exposure time of X-ray expusures made in succession, a. condenser connected through a resistance to a. source of electrical potential during the periods or time to be measured, a an indicating device connected in parallel with said condenser, said device responding only at a predetermined minimum voltage, so that said response takes place only it" a certain total amount determined by the value of the resistance the measured time has been reached.

1%. In for integrally measuring the sum of any desired number of small periods of time and for effecting an indication or actuation after a predetermined adjustable total amount of time has been reached, especially for supervising the total exposure time of Y-ray exposures made in succession, a condenser connected through a preferably adjustable resistance to a source of electrical potential during the periods of time to be measured, and a'rclay connected in parallel with said condenser, said relay responding only at a predetermined minimum voltage, so that said response takes place only if a certain total amount determined by the Value of the resistance of the measured time has been reached.

' 14. Apparatus according to claim 12, in which the device responding at a predetermined minimum voltage comprises, a glow-lamp, a thyratron or the like, having connected in its circuit a relay.

15. In apparatus for making X-ray pictures of parts of the human or animal body, means for producing electrical impulses upon application or pressure variations thereto, means for applying blood pressure variations of the pulse to said impulse producing means, an amplifier having relay of the X-raymachine and an extra-systole trap comprising an amplifying tube having in its mined higher plate circuit a relay intercepting the exposure if in its normal position, the grid of said tube being connected to a condenser receiving a single charge at each normal heart-beat and a deterdouble charge at each double heart-beat or extra-systole, the charge being negative with respect to the grid and the constants of the tube and its charging circuit being so dimensioned, that, by the double charge but not by the single charge, the plate current of the tube is interrupted or reduced to such a low value that the relay in the plate circuit falls back.

16. In apparatus according to claim 15, a condenser connected between grid and cathode of the trap tube, saidcondenser being connected in a. charging circuit comprising a source of direct current, a resistance and a contact of the relay actuated at each heart-beat.

17. In apparatus according to claim 15, a (3011'? denser connected between grid and cathode oiv the trap tube, said condenser being arranged in a charging circuit comprising a source of direct current, a resistance and a contact of the relay actuated at each heart-beat, means being provided to effect, as the relay connected in the charging the condenser connected between the grid and cathode of the trap tube, as the relay arranged in the plate circuit of the trap tube falls back, and means for discharging the condenser between grid and cathode of the trap tube as the exposure relay is actuated.

19. In apparatus according to claim 10, means for intercepting the operation of the apparatus by discharging said condenser.

20. In apparatus for making X-ray pictures of parts of the human or animal body, an X-ray machine having a switching rela a piezo-electric crystal, means for applying force from blood pressure variation of the pulse to said crystal, an

amplifier havingsaid crystal connected in its input circuit and having a relay actuated in synchronism with the heart-beats connected in its output circuit, and an adjustable time delay device connected between the said synchronously actuated relay and the switching relay of the X- ray machine, an exposure key having two circuit making contacts, one of said contacts being connected in series with the switching relay of the contact of the key and a holding contact of the relay itself.

SIEGMUND STRAUSS. LOUIS WEISGLASS. 

